An LTE system can be laterally divided into three layers: physical layer, data link layer, and network higher layer. The physical layer provides its higher layer with data transmission service. The data link layer can be divided into MAC sub-layer, RLC sub-layer, and two service-dependent sub-layers: PDCP protocol layer and BMC protocol layer. The network higher layer is radio resource control (RRC) layer.
In the current LTE standards (RANI #63), the following agreements on aperiodic sounding reference signal (SRS) of downlink control information (DCI) format 4 have been reached:
Two bits are added for sounding reference signal triggering and parameter configuration. The two bits can indicate four states: one indicates no aperiodic sounding reference signal activation and the other three are used to indicate three sets of RRC-configured aperiodic sounding reference signal transmission parameters. And each of the three sets can indicate a combination of the following sounding reference signal parameters: sounding reference signal bandwidth (srsBandwidth), frequency-domain position, sounding reference signal hopping bandwidth (srs Hopping Bandwidth), transmission comb, cyclic shift, duration, and number of antenna ports. In addition, the parameter of sounding reference signal hopping bandwidth is valid when hopping is supported, and the parameter of duration is valid when multi-shot SRS is supported. The other SRS parameters are directly configured by the radio resource control layer.
The parameter of sounding reference signal configuration index (srsConfiguraitonIndex) is signaled directly by the radio resource control layer and is common for all sets of aperiodic sounding reference signal transmission parameters.
It is under investigation whether the number and the index of component carriers (CC) should be indicated by downlink control information format 4.
Aperiodic sounding reference signal triggering information of two bits is always present in downlink control information format 4.
In the prior art, a combination of some sounding reference signal parameters is predefined for dynamic configuration via the three states of downlink control information format 4. Due to the limited number of the states, both the number of parameters in the combination and the adjustable range of each parameter are constrained, thus restricting the flexibility of dynamic configuration of sounding reference signal parameters.